1. Field of the Invention
The present invention relates to a clutching device that is installed in an automatic transmission, such as a multiple-plate clutch or a multiple-plate brake.
2. Description of the Prior Art
An automatic transmission, where a torque converter is coupled with a speed change mechanism that employs planetary gears, is in practical use, and frees operators of automobiles from the complex clutch operations that accompany speed changes. The speed change mechanism includes a plurality of planetary gears, clutchs, and brakes, and acquires a speed change output at a required speed change ratio from the set of planetary gears by varying the engaging combinations for the clutchs and the brakes. The general clutch and brake have a multiple plate structure, arranged wherein are "two support members that rotate relatively to each other while their splines are opposite each other in the direction of the diameter" and "a hydraulic piston mechanism." In the multiple plate structure, friction plates that engage one of the two splines and friction plates that engage the other spline are alternately positioned so as to share a ring-shaped overlapped area, and the piston mechanism, shifting in a direction of a relative rotational axis, imposes pressure on the overlapping plates, and permits that pressure to act on the overlapping portion of the friction plates."
For a clutch and a brake with the above multiple-plate structure, when one of the two members is rotated and the other is stationary while the friction plates are disengaged, the friction plates that are halted will wobble, and make noise, and cause vibrations. This occurs because the friction plate that is halted repeats the movements where, within the range of the wobbling relative to the engaged spline, the friction plates rise due to the rotation of the opposite friction plates and fall due to gravity. A structure that prevents such wobbling and vibration of the friction plates is disclosed in Japanese Patent Application Laid-open No. 2-46324. In this structure, a leaf spring that uniformly forces upward friction plates, which are on the case side of the multiple-plate brake, is provided at the lowest position of the case-side friction plates to prevent the friction plates from falling due to gravity. In a structure disclosed in Japanese Patent Application Laid-open No. 59-137621, a spring member has a large comb shape and is formed by a complicated bending process. Other structures that prevent the wobbling and vibration of a friction plate are disclosed in Japanese Utility Model Application Laid-open Nos. 56-101223 and 2-36631.
Since the conventional structures for preventing the vibration of friction plates absorb the wobbling of stationary friction plates in the direction of the diameter, wobbling and vibration in a rotational direction can not effectively be prevented. Further, as an employed spring member is large and has a complicated structure, the cost of a spring member is high and to hold it a special structure must be additionally provided on the spline side. The attachment of a large spring member is not easy, and before it is removed or mounted, many intervening components must be removed first.
In addition, in a structure that employs a spring member to forcibly press friction plates either in an upward or a downward direction, the friction plates are forced to an eccentric position, and intervals between the edge faces of the friction plates and the spline faces vary. When the friction plates are engaged, due to the variable intervals, an excessive pressure acts on a limited few edge faces and as a result these edge faces are deformed. Thus, the wobbling of the friction plates is increased, and the movement of the friction plates is more eccentric. The eccentricity of the friction plates reduces the service life of the friction plates in the sense that during braking the pressure state varies depending on each of the spline faces around the circumference, and results in uneconomic design because it must require unreasonably high safety rate.